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Single Entangled Photon Creation Unlocked

Photonics.comApr 2012
ATLANTA, April 20, 2012 — A new technique can produce single photons with specific properties more efficiently and about 1000 times faster than the current methods, an important advance for several research areas, including quantum information processing and quantum network development.

Alex Kuzmich, a professor at the Georgia Institute of Technology, and his graduate research assistant Yaroslav Dudin discovered that they could create a Rydberg atom (a highly excited atom that is very near its ionization point) by shining lasers on a dense cloud of rubidium 87 atoms that were laser-cooled and confined to an optical lattice.

The lasers excite one of the rubidium atoms to the Rydberg state, and because of an interesting electromagnetic property of these atoms, exciting one prevents others in a 10- to 20-µm radius from transitioning, an effect called the Rydberg blockade. This ensures that, on average, only one photon will be emitted.

"The excited Rydberg atom needs space around it and doesn't allow any other Rydberg atoms to come nearby," Dudin said. "Our ensemble has a limited volume, so we couldn't fit more than one of these atoms into the space available."

Georgia Tech graduate student Yaroslav Dudin and professor Alex Kuzmich adjust optics as part of research into the production of single photons for use in optical quantum information processing and the study of certain physical systems. (Credit: John Toon)
Once they have an excited Rydberg atom, the researchers use a laser field to convert the energy of the atom into a quantum light field that contains one photon.

The researchers hope to move on to building quantum logic gates between light fields, a great step forward for the fields of quantum computing and networking.

"If this can be realized, such quantum gates would allow us to deterministically create complex entangled states of atoms and light, which would add valuable capabilities to the fields of quantum networks and computing," Kuzmich said. "Our work points in this direction."

The research is also promising for many other areas of physics.

"Our results also hold promise for studies of dynamics and disorder in many-body systems with tunable interactions," Kuzmich said. "In particular, translational symmetry breaking, phase transitions and non-equilibrium many-body physics could be investigated in the future using strongly coupled Rydberg excitations of an atomic gas."

Kuzmich is also doing research on long-lived quantum memories as part of an Air Force Office of Scientific Research Multidisciplinary University Research Initiative headed by Georgia Tech.

The research, reported in the April 19 issue of Science Express, was supported by the National Science Foundation and the Air Force Office of Scientific Research.